Method and apparatus for the measurement of radiation intensity



April 26, 1932. 0. GLAssER ET AL METHOD AND APPARATUS FOR THE MEASUREMENT OF RADIATION INTENSITY v Filed July 1l, 1928 f1. rma

FIG.. 6

2 Sheets-Sheet l dum: m11

April ze, 1932. 1,855,669

METHOD AND APPARATUS FOR THEl MEASUREMENT OF RADIATION INTENSITY o. GLAssER lErAl. 5

Filed July- 1l, 1928 2 Sheets-Sheet 2 dtloz nua @MMA Patented Apr. 26, 1932 nNrrED STATES PATENrgol-"FICE oTTo GLAssEi'u AND VALENTINE E. sEITz, 0E CLEvEL'ANDyoHIo, AssreNoEs vTo, THE VCruavEL-AND CLINre `FOUNDATION, 0E CLEVELAND, omo, A CORPORATION or oHIo' METHOD AND APPARATUS Eon THE MEASUREMENT or EADIATTCN INTENSTTY VApplication filed July l1,

and apparatus forjmeasuring radiation in` tensity.

The object of the invention ,is to provide a comparatively simple, highly eiiicient and accurate device for the purpose described and characterized by having a'detacha-ble part which is'subjectedto the radiation tobe Ine-as*- ured, in contradistinction to subjecting `the 19 entire apparatus to such radiation.

l/Vith this obj ect in view the invention consists in generating, storing and indicating a definite electro-static charge, deta-ching a y, chargecarrying part from the charge generating, creating and indicating means,4 and subjecting the same to radiation for a delinite vperiod of time and then replacing said part and 4indicating the loss which hasl oc- 20 curred during the exposure to radiation. y

combined charging and measuring 1 device for the purpose of indicating the loss of charge which is directly readable upon the indicator.` j i The invention consists also inl the various details of construction and in the manner of combining or arranging the same all of which will be fully; described hereinafter and set forth in the appended claimq" In the drawings forming apart of this specification Fig. 1 is a Vvertical longitudinal sectional view taken through the apparatus and showing the charging device andmeans for indicating the deflection of the string of the electrometer; Fig. 2 is a transverse ver# tical section of the condenser unity and' charging device and Yelectrometer; Figs'. 3 and 4 are enlargedrdetail viewsillustrating different forms of ionization chambers; and Fig. 5 is 'a diagrammaticview illustrating the prin ci'ples of the method4 and apparatus em- The invention consists also in providing al., condenser unit having anvionizatlon cham` indicating device,` the condenser unit beingV 192s,rk 'se-iai no. 291,913. j

pio'yed' in the @frying aber 'our mennen; Y

and Fig. 6 is a'detail v-ofthe yscreen of'an indicating device..

Broadiy Speaking, phamethoaf mappa- ,c

ratusf' involve two parts,.one a condenser to which an ionization chamber is attached,and secondly an improvedt-ype of vstring electrometerincluding, a static generator.v These parts thus broadly mentioned are employed `as follows, theco'n'denserV unit is electrically connected' with theelectrometer unit and the Whole system charged toa knownpotential which isindic'ated on'the electroineter scale.

The condenserunit is then removed and placed with its. ionization chamber in the field of radiation which is `to be measured.

,After the 'chamber'.hasl been exposed for a specified lengthl of time, the condenser unit is again returned or lreplaced upon the elecmeter and thelossof charge due tothe iii ionizationof the air in the'ionization-chamf ,l ber 1s directly read `upon the scale, thus inf dicating theintensity of radiation.`

The condenser 'unit Awith vits `ionization chamber is a; comparatively small vpart Aof the apparatus, and" it alone isplaced'in the `field of radiationl, Consequently the combined f charging deyice, electrometer and f indicating means' are not in Vthe least affected by'y the'ra-V diation` and "cjonse'que'ntly accnracyv of measurernent cangbe obtained.-

*The condenser unit'coniprisesin the'inain ranged centrally within the amberblock A". i. un

Through thisspring member A? theplate A has two"con nections one'with rthe wire Bk mounted 1in the 'tube B and lleading Atof the inner electrode ofv they ionization chamber; The'otherfconnection Cestablishes the 'cong. nectionwbetween thezfpl'ate A andthe charg` ing device and'electrometer. Both of these leads B and'Cy are at all points isurrounded by a1 suitablev dielectric. L

, In practice-weprefer to employ; amberV` plugs B2 at each end ofthetube Bgand inl l which are located the screws to which the wire B is connected. The interior of the tube may be filled with ceresin or any other suitable dielectric as indicated at B3. The lower end of the amber plug B2 is tapered and fitted Vinto the tapered recess formed in the upper end ofthe amber block A4'. The plate A and parts'connected therewith are contained in a suitable casing E and within `this chamber charge. The exterior of. the condenser unit` isat groundlpotential and isconnected with the wallA ofthe ionization. chamber whichis also at ground' potential.

The wire B which leads fromfthe condenser plate Av is connected at its upper end to a screw-or bolt F the. upper end of which is formedr into aV chuck--F to receive. the electrode which extendsintotheionization charnber, this combined screw and` chuck being surroundedby the amber block or` bushing B2, as;` previously described. An amber-lined metal. cap G isfitted upon the upper end of the tube B,.this cap being4 removedwhen the ionization chamber is, placedv thereon.. Ionlization chambersI of different. sizes may be employed 'accordingto theznaturev of the work to .bei done and we have indicated two differy,ent typesand. sizes, a small cylindricalV one H, and a larger'spherical one Leach one havingan .electrode I extending thereinto'and thisffel'ectrode. in. turn extending through an amber: bushing. and; entering the. chuck or connecting member F arrangedfin: the upper endQofth'e tube-B. The' ionization cham- Y b ers-` are of'course made of deflnitesize with walls: ofY definite thickness, and in practice [these chambers have, been made of graphite Vli() is normally at ground potential while the with-.aluminumelectrodesI extending thereinto.'` Y

` Thei elect-rometer isof the.v string type and comprises.anA adjustable attracting plate. J which maybe moved back and: forth byv a screw feedingrv device J ,Y aided by. a springl J rI-his- Vplate Jcanbe m'oved toward or' away front-.the string K as desired'.` The plate J string-.K .and its tubulary support L are at the potential-.ofthe condensing unit previously described. The string K is of very fine platinum wire-fastened.v ati` its upper end toI a metal clip.. M which.- inV turn-is iixedtothe tubular supporting frame L. The lower endv of the Wire: is-cemented to a quartz loop N which Ycan be displaced in aY vertical direction toalter theA con-trolling force on the string. This loop N is compara-tively small and is made of fused quartz. When the string is under tension the loop takes an elliptical form as most clearly indicated. Tension upon the string is had by means of a micrometer screw O on the top of the casing O, this screw being graduated in arbitrary units. The string and mounting are also ixed to a cross slide P which permits lateral movement of the string across the optical axis of theV instrument as hereinafter explained.

` Qxindicates the differential screw which is employed for making this lateral adjustment. This-screw, hovvevemisnotgraduated as the setting Yof the string is made by observing'its image on-the screen R, the shadow of the string Ybeing projected on the graduated ground. glass. of the screen at the end of the horizontal tubular portion R of thejcasing.

' Light for the projectionofthe shadow and for the reading on the scale is supplied by Va lamp: S, preferably a concentrated gas. fuel lamp, mounted in a universally adjustable ball-and-socket receptacle.. In advance. of the light S'- are two cgndenser lenses 'I'. for. illuminating the iield. in the plane ofl the string,l and an objective U is mounted on a focusingy slide in the path of the projected light on the string. In practice we have employed. the lenses and focusing slide'to bring the imageto focus at 'TO c. V1n..distance. The obj'ectivejhas afocal length of lli-xn. 1n. and the workingA distance is somewhat greater. Theobject of using a long focal length lens with a. considerably greater scale distance is .to prevent the string from being attracted to the lens mount which is at ground potential.. A. small defiection of the string. in thedirection ofv thev lens has little eie'ct lon the sharpness-of the image where the'working distanceis large. In order to conserve space the image is twice reflected withinf the tubular h-ood. R. by means ofthe mirrorsV and V2-1nountcd upon spring holders and capable ofadjustment. The tubular portion RV containing the mirrors, objective and scale is approximatelyA 24` c. m. long.4

In the lowerpart ofthe casing O is arrangedthe static generator comprisinga rotary hard rubber tube Wagainst whichV two chamois covered pads X are held by spring tension. The padsupport has attached; to it twocontact springs, Y which electricallyconnect the collector brush to the string system when the crank is turned in a clockwise direction, and ZV which. connects the string to the ground through a suitable resistance leak when the crank is turned-in the opposite direction, thusA allowing perfect control of the stringpot-entialor of the position. Provision may be made for attaching a `dry bulb to eitherthe-upper'or lowerpart of the casing Of in Vorder to absorb any'moisture whichmay be present. By turning the crank inclockwise directiona charge is created or generated and being communicated to the string, the string is deflected due to plate attraction and this movement of the string slight, as it is is graphically indicated upon the graduated screen R through the medium of the lamp S, concentrating lenses T, projector U and refleeting mirrors V and V2.

At the same time that the charge is being generated and the string deflected, the charge is being communicated to the condenser plate A and the entire condenserunit, string and charger will be of the same potential. The

measure of the charge is noW indicated upon the exposure of the condenser unit, ionization of the air in the ionization chamber has taken place, and consequently a proportionate loss v our signatures.

Having thus described our invention, whatl We claim is:

A device of the class described includinga casing, a static electric generator therein, an electrometer in said casing, a screen, means for projecting an image of an indicating member of said electrometer on said screen,

said generator being electrically connected to said electrometer, a condenser unit detachably connected to saidV casing and when attached being in electrical contact with said electro-y meter, said condenser unit including an ionization chamber, and means for sealing a charge in Vsaid chamber when said unitis detached.. n

In testimony whereof, we hereunto aix or'ro GLAssEa v. B. smrz.4

of charge fromthe condenser, and the entire system immediately readjusts itself and indicates the potential or intensity of the charge remaining. The difference Will, of course, indicate the measure of the radiation intensity. Thus, for example, if after charging the entire system the shadow of the Wirerappear's upon the graduated ground glass screen in line with the numeral 50 it indicates that the strength of the charge' is 50 units. After the condenser is removed the shadow of the Wire Y remains in line With the numeral 50,' but after f the condenser unit has been replaced after a definite exposure, the shadow Vof the Wire will be seen to move back a deinite number of degrees, say to 40, thus indicating that l0 units of radiation intensity have been used. I have found that my device is Welly adapted for successful measurements of Roentgen rays, radium rays, etc. over a range of Wave length from 0.02 to 3.0 Angstrom units.

It Will thus be seen that by this method` and apparatus an accurate gauge or Vmeasure of the dose or intensity of radiation can be accurately measured.

It Will of course be understood that'when .the condenser unit isseparated and placed in the zone of radiatiomthe condenser unit per se is not affected by the radiation but the ionization chamber alone is affected'.

While We havevshown anddescribed'an ,y

ionization chamber for use in connection with the condenser unit it Will be understood that some other means than an ionization chamber may be employed such asa photoelectriccell attached to the condenser unit.

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